167 – Tapping Threads in Wood – The Wood Whisperer

uses tapping to learn piano

167 – Tapping Threads in Wood

Video – February 24, 2012

During the construction of my Split-Top Roubo Workbench (which is nearing completion), I was surprised to see Benchcrafted’s plans calling for numerous tapped threads. Instead of attaching the various components of the leg vise using screws or bolts with nuts, they actually recommend cutting threads into the wood! I certainly understood the concept of tapping threads, but I never really considered applying it to woodworking. After picking up some taps and cutting a few myself, I am now a convert! I can just imagine the possibilites in the world of jig-building alone!

Before learning to tap threads in wood, I thought it would be helpful to review other types of mechanical fasteners and why they might not be as good as a bolt in a threaded hole.

Nails are pretty much a brute-force way of holding things together. The nail is driven into the wood, splitting and compressing fibers the whole way. Over time, natural forces cause the wood around the nail to compress even further eventually leading to joint failure.

A step up from a nail is the screw. When you rotate the screw into the wood, it pulls itself in and threads itself into the fibers. The good thing about screws is they are removable, but over the course of years the cut threads become wider and wider and the screw will eventually loosen up.

Threaded Bolts

This is the star of our show today. Once the threads are cut into the wood, you can pretty much remove and replace the bolt as many times as you want and it really doesn’t do any damage to the wood. This is because the bolts threads are sized perfectly to fit into the threads that are cut into the wood. So this is perfect for applications where you may need to loosen and tighten components on a routine basis.

Tapping Threads

All you need to make a threaded hole is a drill bit and a tap. The drill has to be a very specific size and and you can typically find drills and taps in matched sets such as this one. If you need help matching up your bolt, drill, and tap, refer to the handy charts on this page.

Here’s how the system works. The drill bit is used to create the perfect size hole. The tap is then driven into the hole cutting the threads on its way down. You have to be very careful not to strip the threads during this part of the process but in a dense hardwood like maple, you should have no trouble at all. While you might be tempted to use a traditional T-handled wrench for this, I found it much easier to use a power drill at a very slow speed.

One alternative that we can’t forget to mention here is the Tee Nut. These little threaded inserts accomplish the same thing as the threaded bolt technique only instead of actually cutting threads, we simply insert a threaded insert into a hole. They are very easy to use but unfortunately, the way they connect to a workpiece leaves a little to be desired. Over time, the small teeth that go into the wood fibers can break or the wood itself can compress, causing the Tee Nut to lose its grip. So while they can get the job done, I don’t really see them as a good long-term solution.

Products Used

114 – Relative Dimensioning

85 – Duane’s Steamer Trunk (4 of 4)

109 – Birth of a Guitar (Part 2 of 3)

187 – The Knife Block

Nicole’s Wooden Spatula

Chiseling a Corner

81 comments on “ 167 – Tapping Threads in Wood ”

Thanks for this video and the link to the tap set, Marc. I need to get a set for making bottle stoppers. I just couldn’t find the proper size until you posted that link on Amazon.

Great video! I recommend, when tapping soft wood, coating the threads to make them a little stronger. I usally use a wood hardner but even a sanding sealer or poly will work.

Hi Marc, great new video, nice technique, and really nice new website. Very cool.

Great video. Is there any concerns using this method with software woods? Would this work in plywood? Do you have to worry about how much you torque the screw?

I am sure this will work in softer woods, but I imagine you might want to chuck some thin CA glue down there or something to help firm up the fibers. Would be worth experimenting with. Not sure about plywood though. The changing grain directions could very well be an issue.

I have made a leg vise using wooden threads with a metal bolt and the threads were in radiata pine (Australian Softwood) with a 2×4 and have no problems using my grandad’s old tap and dies from the 40’s can put a great amount of toque and has never striped out.
Studies have also shown that clamps made of wood with wooden threads break before the thread strips out, that is the frame breaks before the wooden threads strip out

I’d still be worried it would strip since the threads are so fine. In the past I’ve used ezlok threaded inserts with great success. The threads that touch the wood are a bit more coarse so they hold well and don’t move. I use them on jigs where I’m bolting the workpiece many times since the metal threads are so much more durable than wood threads. Their “soft wood” threaded inserts work perfectly on MDF jigs.

Good movie Marc, and very nice looking closeup!

Interesting way of using machine screws in wood . Like yourself I would never have thought of this method in wood . I’ve used the T nuts and brass inserts before with good results . I do a little metal work so I’m familiar with tapping and threading holes in metal just never thought to use it in wood . I would think in softer woods like pine the threads may not hold up as well over time .

Thanks for doing another great vid .

I am a woodworker and own a fastener company. I have used thread cutting (Type F) and thread forming (Taptite) screws in a few projects with great success. Both of these types of screws eliminate the need for a tap as the end of the screws have features built into them that cut and form up the threads in an existing hole. The fit between the screw and wood is actually better than using a tap and holds well, but I would only use these (or your tap method) in hardwoods as some previous post have mentioned the threads are just not that deep compared to using say a threaded insert. Another consideration is the direction of the load on the joint; the strongest joint will be where the load is perpendicular to the screw (shearing force) and not where the load is inline with the screw (pulling force). One last thought, this should only be used when the joint is adjusted infrequently as even hardwood fibers will fatigue much faster than metal and your screws will eventually strip out.

You described a problem I’ve had with this type of joinery, Matt. It works pretty good when you’re drilling your threaded hole(s) across the grain but when you drill them with the grain, it tends to be weaker. An example of where I’ve tried this was on the bottom of a workbench. I drilled and tapped the ends of the legs and then inserted carriage bolts to make adjustable feet. I eventually had to replace the threads with T-nuts because the wooden threads ripped out.

I guess this underscores how every type of joinery has a right and not so right time to use it. The example you gave, Marc, is a good place to use this kind of joinery but the situation I mentioned wasn’t so great. I’m pretty sure it’s because of the difference in grain direction.

Interesting… I understand the idea that loosening and re-tightening a regular wood screw would degrade the connection over time. But I don’t quite understand why the tee nut inserts, where the part that screws into the wood is never loosened, and where all the adjustment movements are metal-to-metal, why that wouldn’t be preferable to the method you show here, where any adjustment involves the wood-to-metal connection, which is surely more vulnerable to degradation of the connection.

Because the metal prongs can eventually work themselves loose. And the result is the bolt comes out and the tee nut goes with it.

“Because the metal prongs can eventually work themselves loose. And the result is the bolt comes out and the tee nut goes with it.”
…. oh right, sorry… duh… the picture confused me (not hard to do) … the tee nut is only the top bit, the rest is a hanger bolt that might be used with it…

i have seen tee nuts that have 3 holes instead of the prongs, you use 3 small screws to secure it, i like the idea of tapping wood as long as it is something with fine hard grain, softer wood would work but probably wouldn’t last as long and you would need to use as coarse a thread as you could get, also if the tapped hole failed so what just drill it out for a larger size or switch to one of threaded inserts to repair it

Fasteners usually loosen over time because of the “relaxation” that happens in the wood. When you compress wood it will push back (think spring) and it will hold your tee nut. Over a period of time the wood takes a permament “set” and it won’t “spring” back to the original shape. Once that happens bolts will loosen.

It is amazing just how many of you don’t know how to correctly use Tee Nuts. They are designed to fit in a through hole but from the BACK SIDE of the wood so when the bolt goes through the wood it pulls the Tee Nut towards it making a very strong joint with the wood being held between the bolt head and the Tee Nut. The prongs on the Tee Nuts are to keep it from spinning as the bolt is tightened. Tee Nuts are much stronger than any insert, but this is an apples to oranges thing as inserts are a “Blind” fastener meaning that you can’t access the other side of the work piece like perhaps attaching a table top to the frame. There is a good discussion and pictures of Tee Nuts in the current issue of WoodSmith magazine. I hope this helps.

There are some applications where you can’t access the back side or it just isn’t practical to locate the Tee Nut there.

Very good video. You may also want to try drilling a oversize hole then fill with epoxy and drill and tap or wax bolt well and insert in wet epoxy when dry backout bolt and your threads are there. Also if you want tap hole to be true you can put the tap in the drill press and turn the chuck by hand with steady pressure on the quill handle do not power feed.

Marc keep up the great work. I just getting back into woodworking and so glad I found this site

Just curious: What kind of epoxy do you use for filling bolt holes in wood?

I would use West System Gflex or Six10 or Pettit FlexPoxy.

I am still watching old videos and since this has been upgraded I cannot go back beyond the first page. Is it me or the site? Thanks!

Not quite sure what you mean. You are already beyond the first page just by being on this post. If you are trying to get to older videos, you can either use the Previous link under the video post (right above the comments) or you can go to the video archive. With all the things we did change with this upgrade, that is one thing that hasn’t changed. Give me a little more info on exactly what you’re seeing and I might be able to help you a little more.

Marc if you use the video button it list the page numbers but when you click on pages 2-7 it just goes back to page 1. I hope I explained this right

Yeah Jay emailed me and explained. We’re working on it. 🙂

I just saw this in the Jan/Feb issue of ShopNotes. Its on pg 29. Here they were installing set screws to create a snug fit for wooden runners. Take a file and create a v-notch groove perpendicular to and into the threads of the set screw. I guess the idea is to create a self-tapping set screw without the need for a tap and die set.

While we’re doing bug reports… I’ve been unable to unsubscribe from this post… the “manage your subscriptions” page (linked from the notification emails) APPEARS to delete the subscription, but I keep getting notifications, and when I again click through to the manage page, the topic is there again, ready to be deleted again… I’ve “successfully” deleted it about four times now… B-)

Oh now that’s odd. Especially because I don’t see your email as subscribed to this thread either. Maybe it finally took? Let me know.

“Maybe it finally took?” – Yup, it finally took. Fifth time was the charm! B-)

Awesome! I did have to enable and disable the plugin a few times yesterday. That may have been part of the problem. Let me know if you have any other trouble with it. Not that I can fix it, lol. I guess it’s just nice to know. 🙂

There is another method. (aren’t there always?). I know about it because it’s the traditional method of attaching a banjo neck to the banjo rim. It utilizes lag bolts. (screw threads on one end and bolt threads on the other end). The screw end goes into the wood, while the bolt end goes through the second piece and fastens with a washer and nut. You get the best of both worlds, with the screw remaining permanently in the the wood, and the cinching nut with a metal-to-metal contact.
But I like the clean and simple idea of a bolt tapped directly into wood. I’d have never thought to do it–for worry of the bolt stripping out the relatively fragile wood. But I’ve actually never tried it. I’ll add it to my arsenal of techniques. Thanks!

Actually, to avoid confusion, what they refer to as lag bolts in the banjo building circles, are more commonly known as “hanger bolts”.

I’m with Travis above. Threaded inserts have served me well and they are tough to beat, especially if you need to insert and remove the screw more regularly.
The method you showed looked pretty easy though.
Thanks Marc.

I never used those before but they certainly look better than the Tee Nuts I referenced in the video. I’ll have to check them out.

I would be curious to see how long that method of tapping directly into the wood and using machine bolts lasts, especially if it is constantly being loosened and tightened. I was a little disappointed, I was hoping that you doing a video on making threaded wooden dowels/bolts. I think in your application the metal bolts will work, as long as you don’t over-tighten, but perhaps the more substantial threads of a course wooden bolt may be a better match to a threaded wooden hole. I may even suggest using a slightly softer wood for the bolt than the hole, that way the bolt will strip first instead of the carfully postioned hole.

Thanks for the video Marc. As a recovering engineer, I also use threaded inserts with designs in softer metals like aluminum. The larger & coarser threads give more surface area to distribute the load. Helicoil also makes special inserts that have flat sides to give a locking behavior without having to use loctite or helical spring washers. Definitely more expensive to get into inserts than a simple tap because they require specialized taps. One other thing to consider with just tapping directly into the wood is to use a “bottoming” or finishing tap that doesn’t have the taper. Then you you can run threads squarely to the bottom of your hole.

I’ve also used threaded inserts, they work great if you get ones with deep exterior threads. The T-nuts are not so great since they do loosen over time.
You should check out Roy Underhill’s Woodwright’s Shop online videos at UNC PBS to see how the colonials made tapped holes and wooden screws – quite ingenious. In fact his Roubo bench has no metal on it, all wooden vise screws.

I’ve used the threaded inserts for a bunkbed I made for the kids. A word of caution though – don’t use them in end grain. They don’t hold well at all. I ended up using standard bed bolts with barrel nuts – a much better solution!

nice idea never thought wood could be strong enough not to thread. when I have been making adjustable legs I cut off the bottom maybe 2 inches then chisel out the shape of a nut and clue the end back on with the nut inside might try taping next time. seems quicker.

Threads in wood have been around a long time, infact before they were in metal. But usually much larger and courser. You can dig up old shows of the wood wrights workshop for some examples. And I feel if I were to thread wood, I would seek the larger diameter and coursest thread pitch for best result IMO.

A word or two about hangerbolts, I use them a lot as my primary trade as an Electrician. And there are a lot of other lengths, diameters, and pitch than the most common 1/4-20 x 2 1/2″, and can be far more usefully employed when one knows that there are more options. To include what are called “speed nuts” that can recess (enough to get a oket wrench around it) into a piece, and have substantial hold.
http://www.lhdottie.com/pdf%5C. INGBRO.pdf

Or tapping any type or shape of metal you want and mortising it in. I did a basinette for my sister with chunks of brass mortised in and tapped for attachment – in mahogany, it really lends some extra art as custom hardware to the final piece, and not very difficult to work with.

I’ll also second the motion on “bottoming taps”, start with a tappered then finish with a bottoming. Otherwise, when a bolt or screw gets to the tappered portion it will stress the material. And be sure to clean the hole too, debris in the bottom can also contribute to failure, since it is undue pressure that is not being applied to the item being fastened, but lost in the fastening method. Or worse limiting the effectiveness of the fastener, AND contributing to failure or fatigue .

Another issue is torque, and limiting the mount of it suitable to the material, which in the case of wood, is pretty low. I suggest an inch/lbs torque wrench at around 5… Less for smaller fasteners.

I think if I were to tap wood, might shoot for a 3/8-16 (wide and course enough) in a hard dry dense wood, otherwise go for an insert.

Admittedly, I haven’t taken a close look at the Benchcrafted hardware, but I’m wondering if a through bolt and a recessed nut/washer might be a better option? Maybe it wouldn’t be necessary on every threaded connection, but perhaps the parts that will need to be loosened and tightened again (maybe multiple times), like the roller guide at the bottom of the leg?

The reasoning I’m wondering is because as you tighten a bolt, its threads will pull against the threads in the hole and induce stress. The higher the torque level applied to the bolt, the greater the stress will be – in fact, in some cases the bolt itself will actually elongate, such as the connection between the cylinder head and engine block in your car. Obviously, you won’t be pulling out the torque wrench on your bench, but since threads themselves are natural stress risers, and given the natural tendency of wood to split along its grain (as opposed to a homogeneous metal), I’m wondering if repeated tightening might cause the threads themselves to completely shear off and what kind of force would be required to do that.

As usual, there is more than one way to do things, and none are necessarily better than others – just trade offs that need to be understood. This was an interesting video, and if nothing else, you definitely got me thinking (as you always do), and that is always a good thing. Thanks for everything you do, Marc 🙂

1. someone already pointed out… set your block in the drill press, drill the hole, then use the drill press to start the tap.. helps IMMENSELY for keeping the tap straight. 2. Wooden threads tapped are usually better than ones made by CRUSHING the wood fibers to shape. If they are crushed by the insertion of a wood screw, they are on their way to being completely broken by being crushed to shape. 3. If you check out my Facebook page, you will see some piano benches I made.. the legs are attached using a 1/4 20 bolt and a threaded insert. The insert just fills in a hole… not the kind that is on the other side of a piece of wood. large coarse threads buried in oak wont pull out too soon. 4. I agree that if the threads were much coarser and deeper than the bolt you used.. they might last longer. Keep us posted about how the bolt/holes hold up. Thanks for the video.

In the process of my Roubo build with the Guild, I managed to totally screw up a tapped hole. I used a product called PC Wood to fill the hole and re-tap. One thing that I was taught is that, in the process of tapping you should forward the cut, back it off to clear the threads, forward, back off, etc., until you’ve completed the tap. This is supposed to help provide the most crisp threads. It was advice from my Grandpa and may or may not be accurate, but I thought I’d throw it out there. I used his tap and die set to tap my holes.

I think I will stay with threaded inserts (not t nuts). The engineer in me says that if the machine bolt held in wood long term manufacturers would use them. I can’t think of any product that does use machine bolts this way. If the cheap furniture guy could get away with it, they would be doing instead of using hanger bolts and inserts because it would save them money. I guess I would have to see some kind of pullout testing and environment test that allow for wood movement before I buy in.

Backing off every turn is a correct technique in metal to break off the chips in the tap flutes. In metal you can break taps if you do not do this. My thinking is the in wood the chips just don’t hold together enough to require that. If you try this technique with the power driver is steel, you will snap the tap for sure. Grand dad was right.

I am a little concerned since no commercial product I have seen uses machine screws in wood. I just shot an email off to the USDA Forest Products Lab to have their opinion. Who knows maybe we can get a government grant to study this?

Very interesting …
Never thought of doing this … but I have thought of trying it … but I thought that any serious engineer would laugh.

2-things that make this a good option:
1- You are in hard maple
2- Your receiving wood is quite thick and the length of the bolt and the number of threads … are long … and many. With that going for you, I think that this will probably work quite well. You would always want to do this with a coarse thread.

As a general rule of thumb, you do not gain any additional thread strength once you are past a thread depth of 1-1/2 to 2 times the bolt diameter. In other words, a 1/2″ bolt will strip the threads about the same at 3/4″ thread depth as it will at 2″ thread depth. Now this depends on the material of both the bolt and the nut. In wood it is most likely closer to a 1-1/2:1 ratio or less.

Regarding T-nuts, I’ve had good luck with them in situations where I can mount them on the far side of the receiving piece, so the joint stress pulls the prongs in. Thanks to sites like this, I was aware of their tendency to pull out otherwise.

I’m intrigued by what I’ve seen above about threaded wood with threaded dowels for an all-wood connection. I need to come up with a way to work it into my next project.

Hey Marc,
I found that if I used one size smaller drill bit, once the hole is tapped it really holds the bolt securely.

And if I’m planning to keep it (jig, etc..) for awhile, I’ll swab the hole with varnish using a Q-tip.

I’ll have to try that next time!

I agree with threaded inserts. In Aviation engineering, tapped holes can cross-thread or strip over time, and that is with metal. It would be best to use an insert (or invent the floating nutplate for wood) if you want to use a bolt and not worry about the threads. It is much easier to replace an insert than it is the entire section of the bench.

I will be using this to make jigs from here on out. The one thing I did find is that adding a drop or two of CA glue to the threads make them just a little stronger. After the glue drys run the tap back in to clean them up and the treads work just great.

HI Mark nice video, i would add that i like to use the tap in my drill press so i know both hole and tap are at the same 90 degree angle. I do not turn on the drill press i just turn it by hand.

Any thoughts on using this technique to fasten rails of a bed to a headboard/footboard? I have seen people put a nut on the outside of the bed but then you see the nut. If you were able to thread onto the headboard/footboard of a bed would the threads be strong enough to support the rails? hm….. I am definitely intrigued. And if Benchcrafted recommends it I can imagine that it would work well.

I don’t really have enough experience with it to say for sure how well it will work. But it might be worth running a few tests. let us know how it turns out!

I’m a big fan of tapped threads in hardwood, and have been using them for years in harder woods like oak and maple. During one project with white oak, I got so frustrated breaking wood screws for hinges (even steel ones), that I gave tapped threads a try. I remembered reading about it in the Lee Valley catalog; they sold sets of taps and drill bits (not sure if they still do). The catalog mentioned the testing they’ve done that show the tapped threads are often stronger than wood screw threads. And it’s lots easier to tap white oak than is to install threaded inserts in it; the tapped threads are strong enough the inserts aren’t worth the trouble IMHO for fasteners that won’t be repeatedly removed and reinstalled.

So now when I get a set of hinges I throw away the wood screws that come with it, and replace them with machine screws. Tip: for the best fit, if the wood screws were #5, replace them with #5-40 machine screws. It’s an odd size, but most real hardware stores will have them, as does McMaster-Carr online.

Also, I like this drill size chart much better; it’s more complete:

I use the “75% thread” column for wood, or maybe even one number size smaller.

I’m sure someone else will have already mentioned this but one way I’ve tackled this is to drill hole through the piece of wood you want to be the nut. Then widen the top so that it is slightly deeper than the height of a nut that fits the bolt and slightly smaller than the diameter of the nut. Optionally, spread a little quick setting epoxy on the outside of the nut and use the bolt to draw the nut down into the hole. The benefit of this method is you have metal on metal for the thread so wear isn’t such a problem.

If you’re really stuck for cash you can easily turn a bolt into a thread cutter. Just hacksaw a cross into the end of the bolt about 10mm deep and drive it in with a socket wrench. It will easily thread wood, in fact I’ve even tapped aluminium like this.

I built a workshop cart for my workshop in place of a wood workers bench because I am pressed for space. There is not enough room on the bench top face for a wood working vise, mainly because there is a drawer underneath it (poor design I know!).

Could this strategy be used to build my own vise for the front of the bench top? Would wear and tear be an issue from repeated use? The bench top is about 2 1/2 inches thick and is made out of hard maple.

All input is appreciated. Thanks!

When I made my Roubo workbench, I used threaded brass inserts for screws (especially the parallel guide). I wouldn’t even think twice about putting threads in wood no matter how hard it is. Over time it will wear and loosen and there you go. My bench is almost a year old and there have been no problems what so ever. The brass inserts are inexpensive and easy to put in. Metal to metal makes total sense to me!

This is going to sound dorky, but is there any data to show what the life span of a wood thread is as compared to a metal insert type thread? I’m just wondering at what point one makes more sense than the other…or if they are pretty comparable?

In particular I’m thinking about stress, and separately, a case where you may be screwing and re-screwing the connection with some frequency.

I am sure there is some data out there somewhere, but I don’t now where. 🙂

It’s been almost a month since your last video. When do you expect to post the next one?

I can’t wait! Thanks for all your hard work!

Hey Steve. If I ever know the release date of a video ahead of time, you’ll find it posted in our calendar: http://www.thewoodwhisperer.com/calendar/
I have one scheduled this week.

You may not have heard/noticed but we spent the last month dealing with a major DDoS attack on our site so video took a back seat to survival. 🙂

I have been tapping threads into hardwood for some time now with great success. A couple of good tips are to give the new threads a good soak of thin ca glue to petrify the new threads. Just remember that this will swell the wood so be sure to pass the tap through a second time for a clean up pass. I don’t use activator because I want the ca to penateate as deep as possible into the wood. When using tee nuts, a little dab of 5 min epoxy will hold them in forever. itbecomes a little brittle.

After threading the wood a few drops of thin CA glue will substantally harden the wood. After it dries retap to clean up the fuzz.

My dad was a tool and die maker and he spent his life tapping threads. About a year ago I started thinking about it but in wood. Not much info to go on but I saw a few clips on U tube. This summer, once the garage was all cleaned up and the table saw was finnaly set up, tuned up and ready to go, I started experimenting with great results. The only tap I have is for a 1/4-20 screw but that seems to work well. My first project was for a cross cut sled and I did not intend to tap more than one hole, that being the one for the fence to pivot on while it was squared up to the blade. I put in wood screws to hold it, but was frustrated to see the fence kept being out of sqaure. I gave it a day or two to mull over and had decided to tear the whole thing apart and start fresh when I suddenly realized the wood screws were the problem. I don’t have a drill press yet and I would think even a slightly out of plumb pilot hole could make a mess of things. I quickly tapped new holes for 1/4-20 x 1 1/2″ machine screws with socket heads and was amazed. No pulling, no fussing. My fence is sqaure, the cuts have no tear out, and I repeatedly did the flip test with the off cuts. just delightful. I did not use any wax or thread lubricant, and tapped the holes with a standard craftsman cordless drill. What I have learned is you have to go very slow going in. Keep it on low, and set to about 14. Of course, the pilot bit should be done set on high speed and the drill setting. The one difficulty I discovered is that when making through holes the tap is not long enough to easily come out the other side. To make the cleanest holes, tapping straight through until the last threads are clear of the reverse side works best. Then unchuck the bit and pull it out the other side. At least that was what I had seen online. In practice, the wood binds tightly around the unthreaded shank of the bit and there is no way to use a tap wrench to drive it all the way through. In 3/4 stock, there is enough shank in the wood to hold it in there very tightly, and trying to hammer or drive through the tap bit out is useless becuase the top of a tap bit is shaped for a tap wrench, with a slight point. Instead, you could simply reverse the drill, but not so easy. The torque required to get the tap out in reverse as often as not losens the drill chuck and the bit comes out anyway. Once this happens close to the surface of the stock, it is very hard to rechuck. Moreover, you have to back it out very slow and very straight. It is so easy to tip the drill a little bit. In my experiments, I have found a difference in thread quality is noticable in that a degree of slop is introduced and while the screws go in just fine, there is some wiggle. I think the hole gets widened a little bit. On the other hand, if you unchuck the bit and use a tap wrench or a simple cresent wrench to reverse the bit by hand, the holes are excellent with no slop at all. I know it seems like such a small thing, but try it and tell me if you agree with my results or not.
I ended up using machine screws throughout the jig and love it. It makes building them like using an erector set. Adjustments and modifications are limitless. No messing with Tee nuts, and it lends the work such a cool look. I add a countersunk hole with a forstner (?) bit and everything is smooth and flush. Quick too. I can’t imagine going back to just wood screws now.

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